From the article in the technical publication "Der Bauingenieur 51" (The Civil Engineer 51), 1976, page 110, it is known that there are anchoring elements of the types A and B. Anchoring elements of the type A transmit the combined stress from the tension member directly to the compression body. Anchoring elements of the type B transmit the combined stress over a pressure pipe in the compression body.
The A-type anchoring element has the disadvantage that the combined stress presents a peak at the beginning of the compression body and then decreases towards the end proximal to the bottom of the anchor bore. In a rough comparison, it can be said that the combined stress is distributed in the pattern of a triangle with the maximum at the beginning of the compression stretch and tending towards zero at the end of the compression stretch.
The anchoring element of the B type has the same disadvantage, but in the reverse manner, the combined stress has its maximum at the end proximal to the bottom of the bore and tends towards zero at the free end. It is disadvantageous in both anchor types that the combined stress is very unevenly distributed over the anchoring length, so that the anchor may be able to absorb the maximal combined stress.
A prestressable tensioning anchor having an inner rod-like tension member and an outer pipe-like tension member is known from German Pat. No. 20 19 533. Both tension members are connected at their ends facing the bottom of the bore. The opposite ends are connected with tensioning devices. The end facing the bore of the outer tension member is surrounded by a compression body extending over an anchoring stretch. In this known anchoring rod, the disadavantage consists in the fact that the tensioning device which prestresses the inner tension member is supported on the outer end of the pipe-like tension member. When the inner tension member is subjected to initial stress, no forces are introduced into the foundation soil. It is hereby only a matter of an inner state of tension. When the outer tension member is prestressed by means of the tensioning device resting on the foundation soil, forces are introduced into the ground. The maximum peak of the composite tension can be found at the beginning of the tensioning stretch, going towards zero at the end of the tensioning stretch. This known anchor behaves like the anchoring rod of the type A.